Method and apparatus for digitally processing frequently updated images from a camera

ABSTRACT

The invention relates to a method and a system for digitally processing of frequently updated images from a camera. 
     The system comprises at least one camera ( 2 ), at least one display unit, a network ( 6 ) for connecting the at least one camera with at least one display unit, and an image processing means ( 30 ). 
     The image processing means comprises means for defining a first scaling area and a peripheral scaling area, which is enclosing the first scaling area, within an acquired digital image, and means for scaling the peripheral scaling area differently than the first scaling area so that the peripheral scaling area is downscaled in relation to the first scaling area, wherein the first scaling area is uniformly scaled in both a vertical and a horizontal direction.

TECHNICAL FIELD OF THE INVENTION

The present invention relates to a method of digitally processingfrequently updated images from a camera. Further, the present inventionrelates to a system, a camera, and a presentation unit performingdigital processing of frequently updated images.

BACKGROUND ART

Systems for distributing and presenting images from cameras are oftenused in applications for surveillance, inspection, security, and/orremote sensing. Processing of images in such systems is known. Forexample, in U.S. Pat. Nos. 5,185,667 and 5,359,363, there is described adevice for omnidirectional image viewing. The imaging device is based onmathematical correction of a circular image obtained from a fisheyelens. The device is preferably used to provide a wide viewing anglewithout having to rotate the camera that is acquiring the images.

In some situations the distributed images does not fit into thepresentation application and then have to be adapted to the size allowedby the application. Currently, the normal way of making images from acamera suit such an application is to scale down or crop the images tosuitable size. However, by scaling down or cropping the images importantvisual information will be reduced or erased from the presentation ofthe images.

In U.S. Pat. No. 4,605,952 there is described means and a methodfor-providing a television signal format where the increased verticalresolution and the wider aspect ratio of a High Definition Televisionservice can be achieved and where the signal format still is compatiblewith existing standard receivers. The patent document discloses atelevision studio camera provided with processing equipment for changingthe aspect ratio of the image from the camera and for transforming it toa standard definition television image. The change of aspect ratio isachieved by compressing the central part of each line and compressingthe beginning and the end of each line nonlinearly. Then samples fromalternate lines are selected and combined to make up the standardtelevision image.

SUMMARY OF THE INVENTION

One object of the present invention is to reduce the height and width offrequently updated images, which are acquired by means of a camera, andsimultaneously preserve important visual information.

The object of the present invention is achieved by means of a method ofdigitally processing frequently updated images according to claim 1, bymeans of a system according to claim 13, by means of a camera accordingto claim 17, by means of a presentation unit according to claim 21, andby means of a computer program product according to claim 26. Preferredembodiments of the present invention are defined in the dependentclaims.

More particularly, according to one aspect of the invention, a method ofdigitally processing frequently updated images from a camera, comprisesthe steps of defining a first scaling area and a peripheral scalingarea, which encloses the first scaling area, receiving an updated image,scaling the peripheral scaling area differently than the first scalingarea so that the peripheral scaling area is downscaled in relation tothe first scaling area, wherein the first scaling area is uniformlyscaled in both a vertical and a horizontal direction.

An advantage of the method of the present invention is that the qualityof the images are preserved in an area of interest, i.e. the firstscaling area, while the height and the width of the images aredecreased. Further, the visual information of the area of lesserinterest, i.e. the peripheral area, is reduced and not erased. Thisresults in that the portion of the image within the first scaling areais presenting a portion of an image in which objects is fullyidentifiable, while the peripheral scaling area is presenting a portionof an image in which it could be difficult to identify objects, butwhere it at least is possible to recognise a movement of an object.

For example, the first scaling area could be covering a door, while theperipheral scaling area is covering the area surrounding the door. Thus,a person looking at the images is able to visually detect a movement inthe peripheral scaling area. The movement will alert the person and drawhis attention to the image. The person will then be able to identify theobject of the movement when the object enters the first scaling area.

In one preferred embodiment said method is utilised to downscale theimages for presentation of more than one image simultaneously on onedisplay unit. Thus, such an application would save both space and moneywithout reducing the important information of the image.

According to a preferred embodiment of the invention the method furthercomprises the step of dynamically changing the appearance of saidperipheral scaling area in response to instructions for moving theposition of the first scaling area within the image boundaries.

An advantage of this embodiment of the invention is that a personviewing the images from a camera is able to move the first scaling areafor identifying the cause of a movement that have been perceived in theperipheral area or just for changing the area of interest without havingto physically turn or move the camera.

According to another aspect of the invention a system for acquiring andpresenting images of a specific environment for a user, comprises atleast one camera, at least one display unit, a network for connectingthe at least one camera to at least one display unit, and an imageprocessing means. The image processing means of said system comprisesmeans for defining a first scaling area and a peripheral scaling area,which is enclosing the first scaling area, within an acquired digitisedimage, and means for scaling the peripheral scaling area differentlythan the first scaling area so that the peripheral scaling area isdownscaled in relation to the lo first scaling area, wherein the firstscaling area is uniformly scaled in both a vertical and a horizontaldirection.

An advantage of having the image processing means positioned in a devicefor distributing the images to at least one display unit is that sucharrangement saves bandwidth in the network connecting the device fordistributing images with the at least one display unit. A furtheradvantage of this arrangement is that it makes it possible to storenon-processed images for later use at a device for distributing theimages.

The advantage of saving bandwidth also applies to an embodiment wherethe scaling method is implemented in an image processing means in thecamera.

In a preferred embodiment the invention is part of a system forsurveillance, inspection, security, and/or remote sensing.

In the context of the invention, downscaling of an image means that thesize of the image is decreased. A downscale in the direction of X by adownscale factor sx corresponds to a multiplication of the size of theimage in said direction with a scale factor 1/sx.

Further scope of applicability of the present invention will becomeapparent from the detailed description given hereinafter. However, itshould be understood that the detailed description and specificexamples, while indicating preferred embodiments of the invention, aregiven by way of illustration only, since various changes andmodifications within the spirit and scope of the invention will becomeapparent to those skilled in the art from this detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will now be described in more detail with reference to theaccompanying drawings, in which

FIG. 1, is a schematic view of a system in which preferred embodiment ofthe invention is to operate,

FIG. 2, is a schematic view of a camera according to the invention,

FIG. 3, is showing the defined scaling areas, according to oneembodiment of the invention, in an image not yet processed,

FIG. 4, is showing the scaling areas of FIG. 5 when the image has beenprocessed in accordance with the invention,

FIG. 5, is showing an image in the form of a line pattern before it hasbeen processed in accordance with an embodiment of the invention,

FIG. 6, is showing the image of FIG. 5 when it has been processed inaccordance with an embodiment of the invention,

FIG. 7, represents an image from a camera that is used for monitoring anentrance zone of a room,

FIG. 8, is showing the image of FIG. 7 when it has been processed inaccordance with an embodiment of the invention,

FIG. 9, is a schematic view of a scaling means in a preferred embodimentof the invention,

FIG. 10, is a flowchart of a process of the scale factor selector inFIG. 9,

FIG. 11, is a flowchart of a process of a preferred embodiment of thescaling means, which process manages the output signals from the scalingunit of FIG. 9 and compiles the pixels to a complete image for transfer,

FIG. 12, is schematic view of the scaling unit of FIG. 9,

FIG. 13, is a schematic view of the x-direction scaling unit of FIG. 12,

FIG. 14, is a schematic view of the y-direction scaling unit of FIG. 12,

FIG. 15, is a flowchart of a preferred process in the scale factorcontroller of FIG. 13 and FIG. 14,

FIG. 16, is a flowchart of a preferred process in the Pixel in/outcontroller of FIG. 13 and FIG. 14,

FIG. 17, is a schematic view of a system having a video servercomprising processing means for processing an image according to theinvention,

FIG. 18, is showing an image comprising the images from four differentcameras and their scaling areas before scaling,

FIG. 19, is showing an image comprising the images from four differentcameras and their scaling areas after scaling,

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 illustrates a system utilising an embodiment of the invention. Inthe figure there is shown four cameras 2 a-d being connected to apresentation unit 4 via a network 6.

In a preferred embodiment of the system the cameras 2 a-d are sendingfrequently updated digital images over the computer network 6 to atleast one computer functioning as a presentation unit 4. The digitalimages are preferably coded and could for example be coded by using theJPEG standard or any other suitable coding. In the preferred embodimentthe images are either sent as separate files or by means of streaming.At the site of the computer 4 there is provided a control means 8. Thecontrol means is preferably arranged for controlling pan and tiltfunctions of the images. In the preferred embodiment four digital imagesare presented simultaneously on the display device 10 of the computer 4.Thus, saving both space and equipment in comparison with having theimages presented on four separate display devices. Depending on thepurpose of the presentation of the image and/or features of apresentation application it could be advantageous to present just oneimage on the display 10. There could also be reasons to present anynumber of images simultaneously on the display 10.

In FIG. 2, there is presented a schematic view of a camera 2 accordingto a preferred embodiment of the invention. The camera produces an imagestream in which each image is processed. The camera 2 comprises a lens20 for projecting an image of the environment onto an image sensor 22,which, for example, could be of CCD- or CMOS-type. The output of theimage sensor 22 is then processed in an analogue processing means 24 ina way that is known to a person skilled in the art. The output of theanalogue processing means 24 is then forwarded to a digital, processingmeans 26. In the digital processing means 26 the image is processed byan image DSP 28 (Digital Signal Processor), a scaling means 30, and aJPEG compression means 32. The image DSP 28 creates an image fromreceived raw sensor data and processes the image to enhance the qualityby eliminating various types of noise, filtering etc. The DSP 28 couldfor example be a SAA8110G DSP from Philips Semiconductors. The scalingmeans 30 processes the image from the DSP 28 in a manner that will bedescribed later in this document. The image processed by the scalingmeans 30 is then processed in a JPEG compression means 32 for convertingthe image to the JPEG format. Then the output from the digitalprocessing means 26 is passed to a network controller 36, in which theimage is handled by a network protocol stack and sent over the computernetwork 6 via a network interface in the camera 2. The networkcontroller 36 preferably acts as a network server.

Further the network controller 36 is arranged to receive controlcommands from the computer network 6 for controlling the function of thecamera 2 and the image processing functions. One of the control commandsis a command for moving an area of interest used in the scaling means,the area of interest is further explained below. Other control commandscould for instance be commands for changing the scale factors of thescaling areas.

Now referring to FIG. 3 and FIG. 4, the scaling means is arranged toprocess the digital image it receives as input as follows. In thereceived image there is defined logical scaling areas. These scalingareas are an area of interest 101, called a first scaling area, and aperipheral scaling area 102, 103, 104, 105, including a second scalingarea 102 defined as the area above line 112, a third scaling area 103defined as the area below line 113, a fourth scaling area 104 defined asthe area to the left of line 114, and a fifth scaling area 105 definedas the area to the right of line 115. The lines 112 and 113 areextending in a horizontal direction and the lines 114 and 115 areextending in a vertical direction.

The peripheral scaling areas 102, 103, 104, 105 of the image is thendownscaled in relation to the first scaling area. The downscaling of theperipheral area 101 is preferably performed by downscaling the secondscaling area 102, the third scaling area 103, the fourth scaling area104, and the fifth scaling area 105. The second and the third scalingareas 102, 103 are only downscaled in the vertical direction, thusmaintaining the size in the horizontal direction, and the fourth andfifth scaling areas 104, 105 are only downscaled in the horizontaldirection, thus maintaining the size in the vertical direction. Further,the scaling areas 102, 103, 104, 105, of the peripheral scaling area isarranged so that the second scaling area 102 is overlapping the fourth104 and the fifth 105 scaling areas, thus the areas of overlap 116, 119,is scaled in both the horizontal direction and the vertical direction.The same applies to the third scaling area 103 which also is overlappingthe fourth 104 and the fifth 105 scaling areas.

In a preferred embodiment the second and the third scaling areas 102,103are downscaled by means of a factor 5 (scaled by means of a factor ⅕) inthe vertical direction and the fourth and the fifth scaling areas 104,105 are downscaled by means of a factor 5 in the horizontal direction.Further, the first scaling area is not scaled at all. When using thesescale factors and the scaling areas defined according to FIG. 3 theresulting image will have scaling areas of the size showed in FIG. 4.The values of the scale factors for scaling the scaling areas can varyand be of virtually any value. In some applications it could beinteresting to indicate the area of interest in the processed image.This could be made by positioning a frame, e.g. a red line, at theboundaries of the first scaling area or by removing the colourinformation in the peripheral areas, thus resulting in an area ofinterest presented in colour surrounded by a black-and-white peripheralarea.

In FIGS. 5 and 6 the image before and after, respectively, scaling, byusing the scaling parameters of above, is shown. The peripheral areasare scaled by means of a scale factor that is constant during thescaling of each of the peripheral scaling areas. In another embodimentthe downscale factor is changed linearly and increasingly from theboundary of the first scaling area to the boundary of the image.

By using the above mentioned technique for downscaling an image, theportion of the image within the first scaling area is presenting animage in which objects are fully identifiable, while the peripheralscaling area is presenting an image in which it could be difficult toidentify objects, but where it at least is possible to recognise amovement of a object. This is illustrated by FIG. 7 and FIG. 8, whereinFIG. 7 shows a view from a surveillance camera before image processingand FIG. 8 shows the same view after image processing. The interestingarea of the view is the door 180 and, as clearly can be seen in thefigures, the quality of this part of the image is preserved, thus theobjects in this part is not distorted and is clearly identifiable. Theperipheral area is distorted and objects within this area could be hardto identify, however it would be easy to visually detect a movement inthis area.

In a preferred embodiment of the present invention the user is able tochange the position of the area of interest (the first scaling area),e.g. for identifying objects in the downscaled and distorted peripheralarea. To control the change of position the user utilises an inputmeans, such as a keyboard, mouse, joystick etc. The signals from theinput means are transferred to the scaling means were they areinterpreted. Preferably, a signal indicating a movement of the positionto the right results in a movement of the positions of lines 114 and 115in FIG. 3 to the right and a signal indicating movement to the leftresults in a movement of said lines to the left. Accordingly, a signalindicating a movement of the position upward result in an upwardmovement of the positions of lines 112 and 113 in FIG. 3 and a signalindicating movement to downward results in a downward movement of saidlines.

Now referring to FIG. 9, the scaling means 30 comprises a scaling unit310 and a scale factor selector 312. The image source 314, which couldbe the image DSP 28 of FIG. 2, a video camera equipped with someinterface circuitry, etc, generates a stream of pixels from an acquiredimage. The pixels are sent to the scaling means 30 where the scalefactor selector 312 and the scaling unit 310 process them. The pixelsare sent from the image source 314 to the scale factor selector 312 viathe PIXEL IN signal line and when a pixel is available it is signalledto the scale factor selector 312 by means of the PIXIN_AVAIL signalline. The scale factor selector 312 checks the position of the presentpixel and provides the scaling unit 310 with the data of the presentpixel, PIXEL, a signal indicating that a pixel is available,PIXEL_AVAIL, and the scale factors, SCALE FACTOR x and SCALE FACTOR y,to be used for said pixel. The process of the scale factor selector 312is further described below and in FIG. 10. Then the scaling unit 310processes the input values PIXEL, PIXEL_AVAIL, SCALE FACTOR x, and SCALEFACTOR y and produces an output pixel, sent over PIXEL OUT, and a signalindicating that a processed pixel is available, sent over PIXOUT_AVAIL.The resulting pixel stream is then compiled to an output image, e.g. bymeans of a process as described in the flowchart of FIG. 11, and isforwarded to an image destination 316, e.g. the JPEG compression means32 in FIG. 2.

In FIG. 10 the processing of the image in the scale factor selector isdescribed by means of a flowchart. The processing of a new image isinitiated by setting the pixel position variables, XPOS and YPOS, tozero, step 401.

Thereafter, the process checks, step 402, if the present pixel is aboveline 112 in FIG. 3, defining a boundary between scaling areas, orbeneath line 113 in FIG. 3, defining another boundary between scalingareas. If the present pixel is above line 112 or beneath line 113 then ascale factor for the y-direction, SCALE FACTOR y, of the present pixelis set to ⅕, step 403. If the pixel is not above line 112 and notbeneath line 113 then the scale factor for the y-direction is set toone, step, 404. Thus, the input-SCALE FACTOR y to the scaling unit 310of FIG. 9 is set to the value of the scale factor for the y-direction ofthe present pixel.

After the scale factor of the y-direction has been determined, theprocess continues by checking if the present pixel is positioned to theleft of line 114 or to the right of line 115, step 405. If the presentpixel is to the left of line 114 or to the right of line 115 then ascale factor for the x-direction, SCALE FACTOR x, of the present pixelis set to ⅕, step 406. If the pixel is not to the left of line 114 ornot to the right of line 115 then the scale factor for the x-directionis set to one, step 407. Thus, the input SCALE FACTOR x to the scalingunit 310 of FIG. 9 is set to the value of the scale factor for thex-direction of the present pixel.

When both the scale factor for the y-direction and the scale factor forthe x-direction is set, the present pixel is passed to the scaling unitof FIG. 9. This is performed in step 408 by setting the value of PIXELto the value of the present pixel, defined as PIXEL IN.

Then the process tells the scaling unit of FIG. 9 that there is a pixelavailable, step 409, by activating PIXEL_AVAIL once. Then the value ofXPOS is increased by one, step 410, and thereby the present pixel haschanged to be the pixel positioned adjacent to and to the right of thepixel just processed. The new XPOS value is then checked, step 411, forcontrolling whether the value is equal to the number of columns of theimage or not. If XPOS is equal to the number of columns of the image,XPOS is referring to a position outside the image, because the initialvalue of XPOS was set to zero.

If XPOS does not contain a value corresponding to the number of pixelcolumns in the input image, i.e. XPOS defines a column within the inputimage, then the process is returned to step 405 for checking thex-position of the present pixel. If XPOS does contain a valuecorresponding to the number of columns within the input image, i.e. XPOSdefines a column outside the image, then the value of XPOS is set tozero, step 412. Thereafter the value of YPOS is increased by one, step413. The new YPOS value is checked in step 414.

If YPOS does not contain a value corresponding to the number of pixelrows in the input image, i.e. YPOS defines a row within the input image,then the process is returned to step 402 for checking the y-position ofthe present pixel and the process continues processing the new row. IfYPOS does contain a value corresponding to the number of rows within theinput image, i.e. YPOS defines a row outside the image, then the entireimage has been processed and the process is terminated.

FIG. 11 presents a flowchart describing a possible way to compile thepixel stream from the scaling unit to an output image. Initially pixelidentifiers XPOS_O and YPOS_O is set to zero, step 420. Then the processenters a loop, step 422, where the process checks for a signalindicating that a pixel is available. When a pixel is available thepixel, PIXEL_OUT, is stored in an image object, OUTPUTIMAGE, at theposition indicated by XPOS_O and YPOS_O, step 424.

Then the next pixel is to be handled, but first the process has to knowwhether the next pixel is the next pixel in the present row or if thenext pixel is the first pixel in the next row. This is achieved byincreasing XPOS_O with one, step 426, and check if the new value ofXPOS_O is equal to the number of columns in the prospective outputimage, step 428.

If XPOS_O is not equal to the number of columns in the prospective imagethe value of XPOS_O still is within the boundaries of the image andtherefore the process returns to the loop 422 waiting for the next pixelto be available.

If XPOS_O is equal to the number of rows then the process has processedthe last pixel of the present row and prepares to process the firstpixel of the next row by setting XPOS_O to zero, step 430, andincreasing YPOS_O by one, step 432.

Then the process checks if this next row is a valid row of the image,step 434. If the YPOS_O is not equal to the number of rows in theprospective output image, the process returns to the loop 422, becausethen more pixels representing the prospective image are to be expected.If the YPOS_O is equal to the number of rows in the prospective image,the processing of this specific image is finished and the process isterminated.

Now referring to FIG. 12, the scaling operation is performed within thescaling unit by means of a x-direction-scaling unit 330 and ay-direction-scaling unit 340.

The y-direction-scaling unit 340 starts operating on the pixels of thereceived image, the y-scaling unit 340 will be described in more detailbelow. It receives the input signals PIXEL, which delivers the pixels ofthe image, PIXEL_AVAIL, which notifies the y-direction scaling unit thata new pixel is available, SCALE FACTOR Y, which is the y-direction scalefactor produced in the scale factor selector described in FIG. 10.

When the pixels has been processed in the y-direction scaling unit 340,the scaling unit is forwarding y-scaled pixels, PIXEL Y-SCALED, and asignal indicating that a new y-scaled pixel is available, Y-SCALEDAVAIL, to the x-direction scaling unit 330.

The x-direction scaling unit 330 receives these signals and receivesalso an input signal representing the scale factor in the x-direction,SCALE FACTOR X, which is produced by the scale factor selector describedin FIG. 10.

From the x-direction-scaling unit 330 the scaled image is forwardedpixel by pixel via output PIXEL OUT, and each pixel outputted isdeclared available by means of the output signal PIXOUT_AVAIL. Thescaling could also be managed by first processing pixels by means of ax-direction-scaling unit and then processing pixels by means of ay-direction-scaling unit.

Now referring to FIG. 13, the x-direction scaling unit is constructedand operated as a multirate digital signal processing system, suchsystems is further described by John G. Proakis and Dimitris G.Manolakis, 1996, “Digital Signal Processing, principles, algorithms, andapplications”, third edition, chapter 10, Prentice Hall, ISBN0-13-394338-9.

Said scaling unit receives the pixels from the y-direction-scaling unitvia the input signal PIXEL Y-SCALED. The pixels are shifted into theshift register 332, which is part of a FIR-filter (Finite-durationImpulse Response). In order to produce an output pixel, each pixel ofthe shift register is multiplied with a filter coefficient from acoefficient memory 334. John G. Proakis and Dimitris G. Manolakisdescribe how to select coefficients in the above-mentioned book. Eachresult from said multiplication is then added together by means of anadder 336. The result from the addition is then forwarded as an outputpixel, PIXEL OUT. Thus, looking at FIG. 13, the four pixels in the shiftregister 332 is used to calculate one output pixel, PIXEL OUT. The shiftregister 332 can, however, be of any suitable size.

The x-direction scaling unit further comprises a pixel in/out controller337 and a scale factor controller 338.

The pixel in/out controller 337 controls the flow of pixels through thex-direction-scaling unit and it manages the scaling of an image. Thecontroller receives the signal Y SCALED AVAIL from the y-directionscaling unit and uses it to control the reception of pixels at thex-direction scaling unit. The pixel in/out controller 337 produces andsends an address signal to the coefficient memory to declare whichcoefficients to use. The pixel in/out controller 337 also provides thesignal PIXOUT AVAIL when a valid pixel is available. The process of thepixel in/out controller 337 will be further described below inconnection with FIG. 16.

The scale factor controller 338, which is further described below inconnection with FIG. 15, receives the signal SCALE FACTOR X and when thescale factor changes the scale factor controller 338 interrupts thepixel in/out controller 337, and it provides the coefficient memory 334with coefficients and an address representing a storage address of thedesired coefficients. To manage these steps the scale factor controller338 is able to halt the pixel in/out controller 337 by means of the STOPsignal and to store or indicate new coefficients in the coefficientmemory 334 via the signal lines ADDR, DATA IN, and WRITE.

Now referring to FIG. 14, the operation and the construction of they-direction-scaling unit is similar to the operation and construction ofthe x-direction-scaling unit. The y-direction-scaling unit comprisesshift registers 342 a-c, which is part of a FIR-filter. Each shiftregister 342 a-c having a length corresponding to the number of pixelsin one row of the image. The pixels are shifted into the shift registers342 a-c so that the pixels that are in a position in the shift registers342 a-c where they are to be multiplied with a coefficient from thecoefficient memory 344 all are from the same column of the imageprocessed, e.g. in the case of operating on four pixels and if thelatest pixel input, PIXEL, is pixel(x,y) then the pixels outputted fromeach row-long shift register 342 a-c are pixel (x,y−1), pixel (x,y−2),and pixel (x,y−3), respectively. When a new pixel, e.g. pixel (x+1,y),is inputted and the shift registers 342 a-c are shifted, the pixels inposition for output in each shift register 342 a-c are pixel (x+1,y−1),pixel (x+1,y−2), and pixel (x+1,y−3), respectively.

Each pixel in position for multiplication with a coefficient is thenprocessed in the same way as the pixels in the x-direction scaling unitof FIG. 13, i.e. each of them is multiplied with a coefficient and theresult from each multiplication is then added in the adder 346. Theoutput from the adder, PIXEL Y SCALED, is then provided as output fromthe y-direction-scaling unit.

The y-direction scaling unit also comprises a pixel in/out controller347 and a scale factor controller 348. These units operate in the sameway as the units in the x-direction-scaling unit and will be furtherdescribed below.

Both the x-direction scaling unit in FIG. 13 and the y-direction scalingunit in FIG. 14 are using the multirate digital signal processing methodreferred to above. Other methods that could be used are pixel dropping,bilinear interpolation, bicubic interpolation, etc.

In FIG. 15 the process of the scale factor controller, of which one isincluded in the x-direction scaling unit and one is included in they-direction scaling unit, is described.

The process is continuously checking if the scale factor input ischanging, step 502. If a change in the scale factor input is detectedthen the processing of pixels is halted, step 504, by sending a stopsignal to the pixel in/out controller. Then a new set of filtercoefficients is calculated, step 506. Thereafter the new coefficientsare stored in the coefficient memory, step 508. According to anotherembodiment it is possible to use a bigger coefficient memory, capable ofstoring more than one complete set of coefficients. Then the scalefactor controller only has to calculate the coefficients once and storethem all in the coefficient memory. In this embodiment the scalecontroller only has to change the value of the topmost address whenchanging between pre-calculated coefficients. Then the scale factorcontroller releases the pixel in/out controller and the processing ofthe pixels is resumed, step 510.

In FIG. 16 the process of the pixel in/out controller is described. Theprocess in the figure relates to the process of the controller of thex-direction-scaling unit. However the differences between thecontrollers of the different scaling units are small and will beindicated in the following description when such differences arises.

The pixel in/out controller continuously checks if a new pixel hasarrived, step 522. If a new pixel arrives then it is shifted into theshift register 332 of the x-direction scaling unit in FIG. 13, or therow-long shift register 342 a of the y-direction scaling unit in FIG.14, step 524. In the y-direction scaling unit the shift operation alsoshifts the foremost pixel of row-long shift register 342 a into therow-long shift register 342 b and the foremost pixel of row-long shiftregister 342 b into the row-long shift register 342 c, see FIG. 14. Thenan input pixel counter is updated, step 526.

When the counter is updated the process makes a decision regardingwhether a pixel shall be outputted or not, step 528. The decision isbased on the value of the counter and the value of the scale factorindicated by the input signal SCALE FACTOR X in the x-direction scalingunit or SCALE FACTOR Y in the y-direction-scaling unit. In they-direction scaling unit the counter has to keep track of both thepresent row being processed and how many pixels of said row that havebeen processed. Thus, if the scale factor for example is ⅕, i.e. thearea where the present pixel is positioned is to be downscaled using afactor five, then the pixel in/out controller of the x-direction scalingunit makes sure that only every fifth pixel is-outputted. If we use thesame example on the pixel in/out controller of the y-direction scalingunit then the pixel in/out controller makes sure that only every fifthrow of pixels is outputted.

If no output shall be made the process returns to checking if a newpixel has arrived at step 522. However, if an output shall be made thesignal PIXOUT AVAIL/Y SCALED AVAIL is activated, step 530, and the pixelcounter is updated, step 532. Then the coefficient memory address isupdated, step 534, and the process is returned to step 528 for checkingif a pixel shall be outputted. Note that for the y-direction-scalingunit the coefficient memory address is only changed when a new line isto be outputted, i.e. during processing of one line only one set ofcoefficients is used.

Now referring to FIG. 17, according to another aspect of the system, oneor a plurality of ordinary surveillance cameras 3 a-c is connected to avideo server 38. The video server is connected to a computer network 6for transmission of the processed digital image stream to a presentationunit.

Said video server 38 comprises digital processing means 26 includingscaling means 30, which corresponds to the above mentioned scalingmeans, for scaling of the view from the one or the plurality ofthe-surveillance cameras 3 a-c. The digital processing means 26 alsoincludes a DSP 40. The DSP 40 of this embodiment operates essentially inthe same way as the DSP 32 of FIG. 2. However, one great difference isthat the DSP 40 is converting analogue video signals to digital signals.An example of a DSP that could be used as DSP 40 in this embodiment isSAA7111 from Philips Semiconductors. The reference numerals in FIG. 17that correspond to reference numerals in FIGS. 1 and 2 indicate means ofessentially the same functionality and therefore the functions of thesemeans are not repeated.

According to another aspect of the invention a presentation unit, e.g.the presentation unit 4 in FIG. 1, is provided with a scaling meansaccording to the invention. Thus the scaling of the image will beperformed at the destination of an image.

Now referring to FIG. 18, in one preferred embodiment of the inventionfour images is presented on the same display simultaneously. In anembodiment of the invention, e.g. the one described in FIG. 17 or if thescaling is performed within a receiving equipment for monitoring fourimages, the four images 100 a-d is compiled to one new image comprisingall four images as shown in FIG. 18.

In the new image the scaling areas of each individual image are defined.It is then possible to use the same scaling process as described above.The only significant difference is that the process has a greater numberof boundaries to pay attention to during the scaling operation.

The resulting image of such scaling operation is presented in FIG. 19.When the images, i.e. the new image, have been processed it can betransformed to single images again for presentation as separate imagesor they can be kept grouped together for presentation as one image.

1. A method for digital processing a frequently updated image from acamera comprising: receiving at a scaling unit a digital image as adigital representation of the frequently updated image; defining a firstscaling area of the digital image and a peripheral scaling area of thedigital image, which encloses the first scaling area to selectivelycontrol a display of the first scaling area of the digital image at aposition within a display of the peripheral scaling area of the digitalimage; scaling the peripheral scaling at the scaling unit areadifferently than the first scaling area so that the peripheral scalingarea is downscaled in relation to the first scaling area, wherein thefirst scaling area is uniformly scaled in both a vertical and ahorizontal direction; and dynamically changing the peripheral scalingarea in response to instructions for moving the position of the displayof the first scaling area of the digital image within the display of theperipheral scaling area of the digital image.
 2. The method of claim 1,wherein the step of dynamically changing said peripheral scaling areacomprises the step of redefining a position of a boundary between thefirst scaling area and the peripheral scaling area.
 3. The method ofclaim 1, wherein the peripheral scaling area includes: a second scalingarea positioned above the first scaling area, a third scaling areapositioned below the first scaling area, a fourth scaling areapositioned to the left of the first scaling area, and a fifth scalingarea positioned to the right of the first scaling area, wherein the stopof dynamically changing said peripheral scaling area comprises the stepof redefining the position of boundaries of the second, third, fourth,and fifth scaling areas that are adjacent to the first scaling area. 4.The method of claim 1 wherein the defining the first and peripheralscanning areas collectively represent the entire digital image.